We are investigating the structures of several fibrous protein systems - muscle, fibrinogen-fibrin, and microtubules - in order to understand their biological functions at the molecular level. A major objective is the analysis of the molecular basis of muscular contraction and regulation. We are carrying out X-ray crystallographic and electron microscope studies of key muscle proteins, both in the isolated state and in whole muscle. We are also investigating the structure of microtubules, which form highly oriented gels that yield detailed X-ray patterns. A further major goal of this project is the crystallographic analysis of modified fibrinogen, in order to establish the structure of the molecule, and the critical interactions that produce the fibrin clot. BIBLIOGRAPHIC REFERENCES: Cohen, C. The Protein Switch of Muscle Contraction. Scientific American 233, No. 5, 36 (1975). Wray, J.S., Vibert, P.J. and Cohen, C. Diversity of Cross-Bridge Configurations in Invertebrate Muscles. Nature 257, 561 (1975).